Exemplary embodiments of the invention are directed to a method for treating exhaust gas, and arrangement of an exhaust gas system on an internal combustion engine. Specifically, exemplary embodiments of the invention relate to a method for treating exhaust gas of an internal combustion engine, in which less fuel is introduced into at least one first cylinder of the internal combustion engine than into at least one second cylinder of the internal combustion engine. Exhaust gas exiting from the at least one first cylinder is at least partially recycled into an intake air tract of the internal combustion engine. At least the exhaust gas of the at least one second cylinder is supplied to an exhaust gas aftertreatment unit. Exemplary embodiments of the invention further relate to an arrangement of an exhaust gas system on an internal combustion engine of a vehicle.
European patent document EP 2 206 898 A1 describes a method for aftertreatment of the exhaust gas of a multi-cylinder internal combustion engine of a vehicle, in which during low-load operation of the internal combustion engine a first group of cylinders is acted on by fuel, while a second group of cylinders is acted on by less fuel or no fuel at all. An exhaust gas line leads from each of the two cylinder groups to a respective duct of a two-duct turbine of an exhaust gas turbocharger. An exhaust gas recirculation line branches off from each of these two exhaust gas lines, the quantity of exhaust gas flowing through each of these exhaust gas recirculation lines being separately adjustable. The intake air for the internal combustion engine, which is compressed by a compressor of the exhaust gas turbocharger, is supplied to the respective cylinder groups via a separate intake air line, a throttle valve being situated in each of the two intake air lines. During hot operation, the cylinder group, into whose cylinders less fuel, or no fuel at all, is injected, is now acted on by a throttled supply air flow, and an exhaust gas recirculation valve of the exhaust gas recirculation line associated with this cylinder group is opened. In contrast, the exhaust gas of the cylinders of the other cylinder group is not recycled, but instead is returned to the turbine of the exhaust gas turbocharger. As a result, comparatively hot exhaust gas flows through the turbine, and flows further to a catalytic converter.
In this arrangement, a plurality of lines with respective throttle elements is necessary to achieve the desired increase in the temperature of the exhaust gas, which is very complicated.
Exemplary embodiments of the present invention, therefore, are directed to a method and an arrangement of the type mentioned at the outset that allow an increase in the exhaust gas temperature in a particularly simple manner.
In the method according to the invention, an exhaust gas line via which exhaust gas of the at least one first cylinder is suppliable to the exhaust gas aftertreatment unit is at least partially blocked. This ensures that at best, a small portion of exhaust gas originating from the at least one first cylinder, which is operated with a low quantity of fuel or a quantity of fuel that is reduced to zero, reaches the exhaust gas aftertreatment unit. In contrast, the exhaust gas originating from the at least one second cylinder contributes to a greater extent to the temperature of the exhaust gas supplied to the exhaust gas aftertreatment unit. This is achieved in a particularly simple manner, namely, by blocking the exhaust gas line associated with the at least one first cylinder. Thus, separate intake air lines and throttle units for throttling are not necessary for the at least one first cylinder and the at least one second cylinder. Nevertheless, the at least one first cylinder having the injection quantity that is reduced, in particular to zero, makes practically no contribution to the temperature of the exhaust gas.
The effective exhaust gas recirculation rate drops due to the reduction in the quantity of fuel introduced into the at least one first cylinder of the internal combustion engine. This is because for the intake air that is supplied to the at least one first cylinder, less fuel is available that may be converted into exhaust gas. Due to the reduction in the exhaust gas recirculation rate, the soot emissions of the internal combustion engine are also greatly lowered. In addition, a comparatively large quantity of nitrogen oxides is formed which, after oxidation of NO to NO2, is available for oxidizing, for example, soot particles retained in a particle filter. Passive regeneration of the particle filter may thus be achieved in a simple manner. Thus, for the regeneration of the particle filter it is not necessary to additionally provide the internal combustion engine with a metering device for introducing fuel into the exhaust gas.
The temperature of the exhaust gas supplied to the exhaust gas aftertreatment unit may thus be increased in a particularly effective manner. Post-injection into the cylinders of the internal combustion engine may therefore be dispensed with. This is advantageous, since due to the late point in time of such a post-injection, the cylinder walls may be wetted with fuel, which in turn may result in mechanical problems due to the accompanying dilution of the motor oil. In addition, a throttle valve in the intake air tract of the internal combustion engine may be dispensed with, so that the costs associated with such a throttle valve and possible problems with the reliability of such a throttle valve are avoided. The method is thus characterized by particularly high reliability and cost advantages.
However, due to the asymmetrical injection, in which less fuel is introduced into the at least one first cylinder of the internal combustion engine than into the at least one second cylinder of the internal combustion engine, not only it is possible to achieve an increase in the temperature of the exhaust gas in a particularly simple manner, but there is also the option to attain a comparatively high exhaust gas recirculation rate when this is desired. For this purpose, more fuel is then injected into the at least one cylinder, whose exhaust gas is recirculated, than into the at least one cylinder whose exhaust gas is not recirculated.
A particularly simple design of the exhaust gas system may be achieved when, according to one advantageous embodiment of the invention, the quantity of exhaust gas that is recycled into the intake air tract of the internal combustion engine is adjusted by means of an adjusting device that is designed for at least partially blocking or opening up the exhaust gas line. In other words, the adjusting device is used not only for blocking the exhaust gas line, but at the same time is also used as an exhaust gas recirculation valve. A defined distribution of the exhaust gas flow of the at least one first cylinder, which is operated with a particularly small quantity of fuel or no fuel at all, over an exhaust gas recirculation line and the exhaust gas line leading to the exhaust gas aftertreatment unit may be achieved in a particularly simple manner. This makes the method particularly easy to carry out.
It has also been shown to be advantageous when the internal combustion engine is operated in a low to medium load range, so that the exhaust gas line is completely blocked, and the exhaust gas exiting from the at least one first cylinder is completely recycled into the intake air tract of the internal combustion engine. The exhaust gas exiting from the at least one first cylinder then has no influence on the temperature of the exhaust gas which is present upstream from the exhaust gas aftertreatment unit.
This complete recycling of the exhaust gas into the intake air tract may be carried out in particular up to a medium load range of up to 800 Nm, for example, since the exhaust gas recirculation rate is reduced due to the decreased quantity of exhaust gas leaving the at least one first cylinder. In contrast, for an internal combustion engine in which all cylinders are acted on by the same quantity of fuel, complete recycling of the exhaust gas may take place only in a comparatively low load range, for example in a load range of up to approximately 400 Nm, without impairing the operation of the internal combustion engine.
Furthermore, it has been shown to be advantageous when the amount of fuel that is introduced into the at least one second cylinder is greater by the amount of lesser fuel that is introduced into the at least one first cylinder. A torque of the internal combustion engine is thus at least essentially maintained, which is achievable when the quantity of fuel to be provided for this torque is uniformly distributed over the cylinders of the internal combustion engine. Thus, despite the asymmetrical injection, the torque of the internal combustion engine does not decrease.
It is also advantageous when the at least one first cylinder and the at least one second cylinder are each supplied with intake air via the same intake air tract. It is therefore not necessary to provide complicated, separate intake air lines, so that a particularly simple design of the intake air tract is achieved.
In another advantageous embodiment of the invention, the cylinders of the internal combustion engine are supplied with the intake air unthrottled. Namely, providing a throttling device in the intake tract may thus be dispensed with, and controlling the air supply to the internal combustion engine is simplified.
A particle filter as the exhaust gas aftertreatment unit is preferably regenerated when the exhaust gas line is at least partially blocked. It is thus possible to provide an active regeneration of the particle filter, i.e., a regeneration by fuel that is additionally introduced into the exhaust gas but not already combusted in the internal combustion engine, or also a passive regeneration, in which the soot retained in the particle filter is oxidized by nitrogen dioxide.
Lastly, it has been shown to be advantageous when exhaust gas is suppliable to a first duct of a turbine of an exhaust gas turbocharger via the blockable exhaust gas line, while exhaust gas of the at least one second cylinder is supplied to a second duct of the turbine via a second exhaust gas line. It is thus ensured that in any event, exhaust gas from the at least one first cylinder mixes with exhaust gas from the at least one second cylinder, downstream from the turbine. At this location the exhaust gas may be supplied to the two ducts of an asymmetrical turbine in order to provide the internal combustion engine with this compressed intake air over a particularly large operating range.
In the arrangement according to the invention of an exhaust gas system on an internal combustion engine of a vehicle, the internal combustion engine has at least one first cylinder and at least one second cylinder. By means of a control device, the first and second cylinders may be acted on by quantities of fuel that are different from one another. Exhaust gas exiting from the at least one first cylinder is at least partially recyclable into an intake air tract of the internal combustion engine via an exhaust gas recirculation line. The exhaust gas recirculation line branches off from a first exhaust gas line, via which exhaust gas of the at least one first cylinder is suppliable to an exhaust gas aftertreatment unit. The exhaust gas of the at least one second cylinder is suppliable to the exhaust gas aftertreatment unit via a second exhaust gas line. An adjusting device by means of which the first exhaust gas line may be at least partially blocked or opened up is situated in the first exhaust gas line. By means of the control device, asymmetrical injection into the first cylinder and the second cylinder is achievable, and by blocking the first exhaust gas line, primarily the exhaust gas from the at least one second cylinder is supplied to the exhaust gas aftertreatment unit. In this way, comparatively hot exhaust gas may be supplied, even under low load, to the exhaust gas aftertreatment unit using particularly simple means, namely, by utilizing the adjusting device. Thus, even under low load of the internal combustion engine, the exhaust gas aftertreatment unit may be brought to its light-off temperature, at which in particular it substantially converts or treats pollutants contained in the exhaust gas. When the exhaust gas aftertreatment unit is a particle filter, the particle filter may be regenerated by increasing the exhaust gas temperature.
The quantity of exhaust gas that is recyclable into the intake air tract of the internal combustion engine via the first exhaust gas line is preferably adjustable by means of the adjusting device. It is then necessary to provide only one such adjusting device for blocking the first exhaust gas line, and at the same time, for adjusting the exhaust gas recirculation rate.
The advantages and preferred embodiments described for the method according to the invention also apply to the arrangement according to the invention, and vice versa.
The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and/or only shown in the figures may be used not only in the particular stated combination, but also in other combinations or alone without departing from the scope of the invention.